The present invention relates to an internal combustion engine mounted on a small planing watercraft, and more particularly to an oil tank of a four-cycle internal combustion engine with a dry sump lubrication system.
A small planing watercraft is propelled to plane on the water usually by a two-cycle engine which is small in size and light in weight. Since the small planing watercraft is a sporty vehicle, the two-cycle engine which accumulates no engine oil in a crankcase has an advantage that no engine oil flows into a combustion chamber from the crankcase when the small planing watercraft turns over. The two-cycle engine, therefore, is suitable for mounting on a small planing watercraft.
In recent years, however, in view of environmental protection, a four-cycle engine of relatively low noise level and clean exhaust gas has been examined for mounting on a small planing watercraft. For engines of this type also, attempts are being made to apply a dry sump lubrication system wherein no engine oil is accumulated in the crankcase.
One of the attempts is disclosed in JP-A-7-237587. The publication shows a small planing watercraft and, mounted thereon a four-cycle engine for propelling the watercraft. An oil tank accumulating engine oil for lubricating the engine is located in a space above a coupling which interconnects an engine output shaft and an impeller shaft extending in a longitudinal direction of the hull. An oil pan formed at the bottom of the engine body and the oil tank are communicated with an oil pipe, and the engine oil collected in the oil pan is transferred to the oil tank through the oil pipe by means of an oil pump.
When the dry sump lubrication system is applied to the internal combustion engine of a small planing watercraft, a problem to be examined is where and how to mount the oil tank in a limited space. In particular, when the oil tank is separately mounted from the engine body, it is important to determine a mounting location and mounting manner of the oil tank so that the oil tank can be secured firmly, and mounting and dismounting of the oil tank as well as maintenance of the oil can easily be performed.
The oil tank shown in the above publication is mounted separately from the engine body, but the publication does not disclose any means for mounting the oil tank except for the rough mounting location (above the coupling) of the oil tank, and it is not clear on which structural member the oil tank is mounted, and how to perform the maintenance of the oil. The coupling used in a small planing watercraft is associated with rubber elements or the like, and requires relatively frequent maintenance and inspection. Therefore, the oil tank located above the coupling hinders the maintenance and inspection of the coupling.
The present invention has been developed in view of the above problems which have been posed when a four-cycle engine with a dry lubrication system is mounted on a small planing watercraft.
Accordingly, it is an object of the present invention to provide an engine of a small planing watercraft having advantages of the dry sump lubrication system.
Another object of the invention to provide a dry sump lubricating system, having an oil tank which is easy for inspection of the oil level and replenishing of the engine oil, and is easy for dismount, cleaning, and replacement of the engine oil, and is stably mounted.